Telegraphy



Patented Jan. 28, 1930 UNITED STATES HOWARD D. COLMAN, OF ROCKFORD, ILLINOIS TELEGRAPHY No Drawing. Application filed April 17, 1926, Serial No. 102,813. Renewed November 16, 1928.

The invention relates to telegraphic communication, and its general aim is to lower the cost of such communication.

The cost of telegraphic communication depends to a large extent upon the length of time required in the transmission of the message matter, and the time required in turn depends largely upon the number of current impulses which must be transmitted to-represent such message matter. The present practice is to transmit ordinary message mat ter by the use of code combinations constituting signals which represent the letters of the alphabet, these signals being used collectively or in groups to spell out the words letter by letter. Thus the number of impulses which must be used to transmit a word depends directly upon the number of letters in the word, and the number of impulses required in the case of the average word constitutes a fixed limitation upon the capacity of a telegraph system for handling message matter.

The object of the invention is to overcome such limitation upon the line capacity by the use of signals constituted independently of the letters composing words represented thereby, to the end that the number of im pulses which are required to be transmitted to represent ordinary message matter may be substantially reduced.

In transmitting a message according to my invention, I employ jointly word and letter codes whereby such words of a given message as are commonly used in average daily intercourse are transmitted by means of signals individually representing such words and composed of code combinations of a relatively small number of units capable of being represented by either positive or negative or current and no current impulses; and whereby the remaining words of the message are transmitted letter by letter by means of signals representing letters of the alphabet.

The great majority of the words used in average daily intercourse may be transmitted by means of word signals, with a substantial saving in line time as compared with the methods now in use, and only words which are normally used with less frequency, proper names, and the like, need be transmitted letter by letter. All of the signals of the word code and of the letter code are made of a particular kind or character. For example I employ in the present instance signals of uniform length, that is to say, composed of the same number of units. This renders it unnecessary to use space signals between word signals and between word and letter signals, all of the signals being distinctive in character and capable of being distinguished from each other when following in direct succession. The only instance in which a space signal is required is between two words transmitted letter by letter and following in succession.

Proceeding now to a more detailed consideration of my invention, the word-code signals are composed of combinations of an equal number of units having two or more interchangeable differentiating characteristics. Thus, they may be of the general type now commonly used in the Baudot code, wherein each unit has two differentiating characteristics and is represented by either a positive or negative impulse. The number of units employed in each of the word-code signals is determined by the number of different code combinations to be provided, or in other words, by the number of words comprising the limited vocabulary. In practice, the number of words comprising such vocabulary may be determined on the basis of the frequency with which words are used in daily intercourse. An investigation made for this purpose disclosed that in a file of ordinary incoming business correspondence the 32 most frequently recurring words were found to be used approximately 47% of the time; 1000 words approximately 91% of the time; and 2000 words approximately 96% of the time.

Assuming, for the sake of illustration, that the prearranged vocabulary of words to be transmitted by means of word-code signals contains 2000 words, the desired number of different code combinations may be obtained by the use'of 11 units, each capable of being represented by either a positive or negative current impulse. This is in accordance with the known mathematical formula p Where N represents the number of units in each code combination and p the number of different characteristics by which each unit may be represented. The use of 11 units gives, according to the formula, 2048 combinations.

To avoid the necessity for using space or other special signals between word-code signals and letter-code signals, the latter are in accordance with the. present embodiment of my invention composed of the same number of units as the word-code signals. Thus in the instant case above referred to, in which code combinations of 11 units are employed, giving a total of 2048 combinations, a suflicient number of these code combinations are first assigned to the letters of the alphabet and other characters, and to a space signal,

and the remaining combinations are assigned to the individual words of the prearranged vocabulary. For example, 48 code combinations may be reserved for the letter-code, including a space signal, and the remaining 2000 combinations individually assigned to the 2000 most frequently recurring words.

It will thus be apparent that a distinctive code combination is assigned to each of the signals, whether word or letter signals, so that it is possible to distinguish these signals one from the other without the use of any space signal between them; and it is only necessary to employ a space signal to distinguish between two succeeding words transmitted in accordance with the letter-code. However, inasmuch as the great majority of words are represented by word-Code signa s,

the occurrence of two words in succession which must be represented by letter-code sig nals will be the exception rather than the rule, so that the use of a space signal will not be necessary except upon infrequent occasions.

To illustrate the saving eifected by my invention, it may be assumed, in accordance with the foregoing, that 11-unit code com.- binations are provided for both the word and lettercodes, and that a message containing 100 words is to be transmitted. Since on the basis of the above mentioned investigation 96 of these words would fall within the given vocabulary, the transmission of word-code signals representing them would require 1056 impulses. The 4 remaining words which may be reasonably assumed to have an average of 7 letters each, would require 308 impulses plus a maximum of 3 space signals or 33 impulses,

provided that these 4 words follow in succes-v sion. In other words, 96 wordsignals of 11 units each would require 1056 impulses, 4 words of 77 units each wouldrequire 308 ime pulses, and 3 space signals of 11 units each would require 33 impulses, or a total of 1397 impuises. If the 4 words transmitted letter by letter are each interposed between word signals no space signals would be requiredand the total number of units employed would be 1364.

In transmitting a group of 100 words averaging 5 letters each by the use of the Baudot code, it is necessary to send 25 impulses for the letters of each word, or 2500,

and 5 impulses for each of the spaces between the words, or 500, making a total of 3000 impulses.

Thus it is evident that by means of my invention the capacity of a telegraph system for transmitting message matter is more than doubled as compared to the Baudot codal system.

The substantial elimination of space signals is essential, it will be observed, to the practical carrying out of my invention. Thus, it will be apparent, that if it were necessary to employ space signals between each of the word signals, or space signals between each of the letter signals no substantial saving would be effected.

. While any preferred method may be employed for coding and decoding the signals, it is contemplated that automatic mechanisms will be used for this purpose, but inasmuch as these mechanisms form no part of this invention it is deemed unnecessary to illustrate and describe them herein. It should be noted, however, that the use of such automatic coding and decoding mechanisms is greatly facilitated by the fact that the signals are of uniform length.

In so far as the transmission of the signals is concerned, it will be apparent that existing apparatus may be employed, except, of course, that instead of sending 5-unit signals, it must be adapted to send signals containing a larger number of units, such, for example, as ll unit signals.

The present invention is another embodiment of the generic invention disclosed and claimed in my co-pending application Serial No. 102812, filed April 17, 1926.

I claim as my invention:

In a telegraphic communication system in which signals each composed of a direct succession of units having two or more difierentiating characteristics are transmitted electrically, the method of signalling which consists in transmitting word signals each hav-. ing the same number of units and individually representing such words as fall within a given vocabulary, transmitting letter signals each having the same number of units as the word signals and individually representing letters of the alphabet to spell out letter by letter such words as fall outside the given vocabulary, and sending a space signal be.- tween the adjacent terminal letter signals of successive non-vocabulary words.

In testimony whereof, I have hereunto afiixed my signature.

HOWARD D. COLMAN. 

